The present invention generally relates to an internal combustion engine having a mass airflow based control system and, more particularly, to such a mass airflow based control system which is capable of predicting cylinder air charge values during transient conditions.
Internal combustion engines having mass airflow based control systems are known in the prior art. Such systems typically include a mass airflow sensor located in the engine induction passage upstream from the throttle valve and the intake manifold. The airflow sensor serves to generate signals related to the air mass flow passing through the induction passage.
When a sudden change in throttle valve position occurs, a sudden change likewise occurs in the air mass flow passing through the induction passage, the air pressure within the manifold, and the air mass flow inducted into the cylinders. For example, when the position of the throttle valve changes from a substantially closed position to a substantially opened position, indicating that the operator is demanding maximum torque, a sudden increase in the amount of air mass flow passing through the induction passage occurs. Increases in the air mass flow passing into the cylinders and the pressure within the intake manifold also occur.
When the throttle valve position suddenly changes to allow more air to pass through the induction passage, a period of rapid transition occurs during which the air mass flow passing through the induction passage exceeds that of the air mass flow inducted into the cylinders. The excess air passing through the induction passage but not going into the cylinders remains in the intake manifold causing an increase in manifold air pressure. However, after a steady state condition is reached, the air mass flow passing through the induction passage is substantially equal to the air mass flow passing into the cylinders.
Prior art mass airflow based control systems control the air/fuel ratio based, at least in part, upon cylinder air mass flow values. Those control systems do not directly sense the air mass flow passing into the cylinders, but approximate same from sensed induction passage air mass flow values. However, during non-steady state periods, when the air mass flow passing through the induction passage is not equal to the air mass flow passing into the cylinders, errors occur in the approximation of the air mass flow passing into the cylinders. Attempts have been made in the past to accurately approximate cylinder air mass flow values during non-steady state periods, but those attempts have generally not been successful.
Cylinder air charge values, which are derived from cylinder air mass flow values, have also been employed by prior art mass airflow based control systems in controlling the air to fuel ratio. Attempts have likewise been made in the past to accurately approximate cylinder air charge values during non-steady state periods, but those attempts have also been generally unsuccessful.
Accordingly, there is a need for an internal combustion engine having an improved mass airflow based control system which is capable of accurately approximating either cylinder air mass flow or cylinder air charge values during non-steady state periods.